1. Field of the Invention
Embodiments of the invention generally relate to the field of semiconductor manufacturing processes and devices, more particular, to methods of surface activation by plasma immersion ion implantation process utilized in silicon-on-insulator (SOI) structure.
2. Description of the Related Art
Semiconductor circuit fabrication is evolving to meet ever increasing demands for higher switching speeds and lower power consumption. A higher device switching speed at a given power level is desired for applications requiring large computational power. In contrast, a lower power consumption level at a given switching speed is desired for mobile applications. Increased device switching speed may be attained by reducing the junction capacitance. Reduced power consumption may be attained by reducing parasitic leakage current from each device to the substrate. Both reduced junction capacitance and reduced parasitic leakage current is attained by forming devices on multiple silicon islands formed on an insulating (e.g., silicon oxide) layer on the semiconductor substrate. Each island is electrically insulated from all other islands by the insulating layer. Such a structure is called a silicon-on-insulator (SOI) structure.
SOI structures may be formed in a layer transfer process in which a crystalline silicon wafer is bonded to the top of a silicon oxide layer previously formed on another crystalline silicon wafer. FIGS. 1A-G depict an exemplary conventional method for fabricating SOI structures on a substrate. A donor substrate 102 and a handle substrate 104 are utilized to form SOI structures, as shown in FIG. 1A. A thermal oxidation process may be performed to form a silicon oxide layer 106 on the surface and/or the periphery of the donor substrate 102, as shown in FIG. 1B. An ion implantation process may be performed to implant ions, e.g., hydrogen ions, into the donor substrate 102, thereby forming a cleavage plane 108 at a predetermined depth below the surface of the donor substrate 102, as shown in FIG. 1C. Subsequently, an O2 plasma surface treatment process may be performed to form activated surfaces 112, 114 on both the donor substrate 102 and handle substrate 104, as shown in FIG. 1D, promote the bonding energy at the interface. The activated surfaces 112, 114 are abutted together by flipping the silicon oxide surface the donor substrate 102 over to adhere to the surface 114 of the handle substrate 104, as shown in FIG. 1E. The activated surface 112 of the donor substrate 102 is therefore bonded to the activated surface 114 on the handle substrate 104, as shown in FIG. 1F. In a final step, the donor substrate 102 is split along the cleavage plane 108, leaving a portion of silicon layer 110 and the silicon oxide layer 106 adhered to the handle substrate 104, as shown in FIG. 1G. The silicon layer 110 and the silicon oxide layer 106 bonded on the handle substrate 104 form the SOI structure.
During substrate bonding process, several problems have been observed. For example, interface surface particles, surface imperfections, contaminants, or air trapped at the substrate interface may result in poor adhesion and bonding failure between the donor and handle substrates. Poor adhesion and bonding failure at the interface may affect the mechanical strength and electric behavior of the devices built on the substrate, thereby causing poor device performance and/or failure, along with adversely affecting device integration.
Therefore, there is a need to improve bonding of substrates in SOI fabrication.